The present invention relates generally to scroll compressors and, more particularly, to a method and apparatus for machining a matched set of scroll members for use in such compressors, thereby ensuring proper sealing between respective wrap surfaces of the scroll members during compressor operation.
A typical scroll compressor comprises two facing scroll members, each having an involute wrap, wherein the respective wraps interfit to define a plurality of closed compression pockets. When one of the scroll members is orbited relative to the other, the pockets decrease in volume as they travel between a radially outer suction port and a radially inner discharge port, thereby conveying and compressing the refrigerant fluid.
It is generally believed that the scroll-type compressor potentially offers quiet, efficient, and low-maintenance operation in a variety of refrigeration system applications. However, several design and manufacturing problems persist. For instance, the operating efficiency of the compressor depends upon the integrity of axial and radial sealing between the scroll members. One type of leakage that can occur is between compression pockets of the scroll compressor at those locations where the wrap walls sealingly contact each other to define the boundaries of the moving compression pockets.
The aforementioned leakage is attributable to both the extent to which the machined wrap surfaces of the scroll members exactly follow or fit one another, and the pressure of the compressed refrigerant in the compression pockets, which tends to cause slight radial separation of the scroll member. The latter problem of a separating force during compressor operation has been effectively dealt with by a variety of radial compliance mechanisms in the prior art, e.g., a conventional swing-link radial compliance mechanism. The problem of fit between the wrap surfaces relates to how the scroll members are manufactured and, more specifically, how closely their respective machined wrap surfaces follow the same true involute form so that a radially inwardly moving line of contact is maintained between the surfaces during compressor operation.
Conventional scroll machining practice has been to use a numerically controlled profiling machine, or NC machine, to cause a milling tool and a work piece to undergo relative movement according to mathematical equations descriptive of an intended or desired involute curve. In one such machining system, a two servo controlled cartesian axis machine directs a milling cutter around the involute curve. However, deviations of the milling cutter from the involute path occur due to errors in the movement of the machine caused by constantly changing forces against the two cartesian axes and time lags in the servo response of the drive motor.
Another NC machine system for manufacturing individual scroll members, disclosed in both U.S. Pat. No. 4,893,971, issued to Watanabe et al, and Japanese Laid-open Patent Publication No. 62-88507, involves the simultaneous rotation of the workpiece and linear movement of the milling tool in order to map out an involute curve. While this type of system eliminates some of the errors in movement of the machine due to changes in direction of slide members, each machine exhibits its own systemic deviations and random deviations may occur during each cycle of a particular machine.
In each of the aforementioned methods of manufacturing scroll members, fixed and orbiting scroll members are paired after they have been independently manufactured on the same or different machines. Despite theoretical matching of the complementary fixed and orbiting involute forms, and theoretical repeatability of the machining systems creating them, in practice the fixed and orbiting scroll members must be sorted in order to achieve the best possible fit. Even then, a run-in time for the compressor is often necessary in order to work off high points on the respective wrap surfaces that are not complementary.
The present invention is directed to overcoming the aforementioned problems associated with prior methods of machining scroll members for use in scroll compressors, wherein it is desired to provide a matched set of fixed and orbiting scroll members without sorting or requiring a run-in period for the compressor.